In rapidly quenched amorphous alloys of (Fe_Co_x)_P_C_7 and (Fe_Co_x)_Si_B_, it was found that the zero magnetostrictive alloys are remarkably soft magnetic materials, while the magnetostrictive alloys have rather large coercive force. To investigate the effect of magnetostriction on the properties of the B-H loop, some fundamental magnetic properties in these alloys were studied. The magnetic domain pattern observed by Bitter\u27s method shows a periodic domain structure consisting of 180° and maze domain walls (the periodicity can be seen along the specimen long axis) in all the magnetostrictive alloys, suggesting the existence of magnetic anisotropy whose easy axis varies locally. The estimated value of the anisotropy energy varies with x similar to the composition dependence of magnetostriction. Torque measurements support the above estimation. The coercive force also varies with x and is nearly proportional to the magnetostriction to magnetization ratio. It is, therefore, considered that the anisotropy is caused by the anisotropic internal stress field, and that the stress fluctuation which inevitably exists is responsible for the large coercive force
